Hyperfine fields and electronic structures were calculated by the KKR method to investigate the effects of the X atom on the magnetic properties of Co2MnX. The obtained magnetic moments of Co or Mn sites in Co2MnX are in good agreement with the experimental ones. Though the obtained hyperfine fields on Co or Mn sites are smaller in absolute value than the experimental ones, their trend is consistent with the experimental one. The hyperfine field on Mn sites is essentially determined by the magnetic moments on Mn sites themselves, but not that on Co sites. The relationship between the Co hyperfine field and the valence electron number of X atoms is discussed in terms of the obtained density-of-state.

Hyperfine fields have been calculated by the LMTC-ASA method within the framework of the LSO approximation. The hyperfine field at the Co position in CO,= changes drastically with the T atom from a positive value for the caSe T = Ti to a negative value lor the case T = Fe. The change OCCUK mainly in the contribution to the hyperfine field from valence s electrons (Hvnl), which is sensitive to the neighbouring magnetic moments. The value of H,, is roughly proportional to the 'spin polarization'ol the valence s electrons at CO atom positions, which is closely related to the density of states of valences electrons CO -65.61 100.57 34.96 Co;TiGa Ti 20.35 -68.61 -48.26 Ga 0.00 -4.49 -4.49 CO -90.79 148.04 57.25

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To study the effect of the surface on the shape memory and magnetic properties, we calculated the electronic structures of the films of Ni2xMn1-xGa. Comparing the total energies for the cubic and the tetragonal structure, we found the tendency that the shape memory property may not be preserved in thin films but is recovered with increasing thickness or increasing Ni composition. It was also found that the magnetic moments on Mn are largely enhanced at the surface.

The Heusler type alloys Ni2+xMn1-xGa are shape memory alloys and the phase transition temperature between a tetragonal and a cubic structure becomes higher with increasing Ni composition. To investigate the characteristic properties, the electronic structures of Ni2+xMn1-xGa were calculated for the cubic and the tetragonal structure. We found that the total energy difference between the cubic and the tetragonal structure becomes larger with increasing x, that is, the tetragonal structure becomes more stable. This tendency suggests the fact that the phase transition temperature becomes higher by substituting Mn with Ni in Ni2+xMn1-xGa.